The present invention relates generally to cooling of electronic devices and, in particular, to cooling electronic circuit cards.
In conventional electronic devices such as, for example, computer systems, electronic components are mounted on circuit cards, which are assembled into electronic circuit card modules. The circuit card modules are usually inserted into a chassis of an electronic device and, typically, plugged via a connector into an enclosure having a backplane or a motherboard. The circuit card modules may also include additional circuit cards, which are called mezzanine cards. The mezzanine card is electrically connected to the main card via a connector.
There are several standards defining properties of circuit card modules, for instance, VMEbus, SEM-E, PCI, cPCI standards, etc. The standards encompass mechanical specifications such as card dimensions, connector specifications, etc, along with electronic specifications such as bus structures, signal functions, timing, signal voltage levels, and master/slave configurations. These specifications enable different modules of the same standard supplied from different manufacturers to plug into any enclosure of the same standard, and provide for communications between different modules.
Proper cooling of electronic components in general, and those mounted on circuit cards in particular, is essential in electronic devices, wherein excessive heat generated by the electronic components can cause malfunctions and failure thereof. Depending on the manner of cooling, conventional circuit cards and, consequently, circuit card modules, are generally classified under convection cooled and conduction cooled types. In general, in the framework of the same standard, conventional convection and conduction cooled card modules are different in construction, however, both meeting the same standard electronic specifications.
Convection cooled card modules are mounted within chassis of an electronic device in such a way as to allow the free flow of cooling air over electronic components to dissipate excess heat generated. The flow of air is usually provided by fan.
One example of a conventional convection cooled card module of VME64 standard is shown in FIG. 4 of the drawings. The card module shown in FIG. 4 comprises a circuit card A having a front surface B and a rear surface C, at least the front surface bearing electronic components D. The card module further comprises a standard VME interface front panel E mounted to the top of the circuit card A, including extractors F, alignment pins G, and keying provisions H for the insertion of the module in a chassis of an electronic device; and two VMEbus connectors I and J mounted to the bottom of the circuit card A, for the connection thereof to an enclosure that also conforms to the VME64 standard. The main card shown in FIG. 4 also comprises a stiffening rib provided therealong to inhibit vibration of the card in use.
FIG. 5 illustrates another example of a conventional convection cooled card module meeting the same VME64 standard, which in addition to the circuit card A, comprises a mezzanine card K which has electronic components L.
Convection cooled card modules can typically not be used when there are severe requirements for protection of their cards from harsh environment such as sand, dust, humidity, etc. They also cannot be used in closed electronic devices where air ventilation is impossible.
Under the above conditions, conduction cooled card modules are conventionally utilized. In such modules, heat generated by electronic components of a circuit card is absorbed by an internal heat transmitting layer thereof, often made of copper, and thereby forwarded to a dissipation device, being commonly called a heat sink. The function of this device is usually fulfilled by the chassis in which the modules are mounted. Since a conduction cooled circuit card does not require an air exchange over its electronic components, it may be hermetically sealed within its module or rather used in a sealed electronic device, as it happens most often.
However, in conventional conduction cooled modules, the amount of heat that may be withdrawn from electronic components is rather low (about 15-20 watt), in view of which measures are taken to ensure that these cards and their components can withstand high temperatures. This essentially increases the costs of production of conduction cooled modules and, consequently, their price.
Various attempts have been made to improve conduction cooling in conduction cooled circuit cards by providing a plurality of special heat withdrawing devices for their physical attachment to electronic components of the conduction cooled cards. However, this requires connecting the devices to the dissipation device, which may need accurate machining, is time consuming and, particularly, is not suitable for mass production.
Accordingly, it is an object of the present invention to utilize a standard convection cooled circuit card for the production of a novel conduction cooled circuit card module.
According to one aspect of the present invention, there is provided a conduction cooled electronic card module comprising a circuit card of a convection cooled type of the same standard, having front and rear surfaces and two opposite edges adapted to be received in a chassis of an electronic device. At least the front surface of the circuit card carries electronic components, at least a part of which is capable of generating heat during operation of the module. The rear surface of the circuit card is adapted to be in thermal contact with said chassis at an area of the surface adjacent said edges, when the module is inserted therein. The module further includes a thermally conductive frame on which said circuit card is mounted, so as to be in thermal contact with at least said part of the electronic components and with an edge area of the front surface of the circuit card, adjacent said edges. This enables the heat generated by the electronic components of the circuit card to be transferred to the frame and therefrom, via the edge areas of the front and rear surfaces of the card, to the chassis.
Preferably, the circuit card is provided with a thermal vias at the edge areas thereof. This facilitates the hear transfer from the front surface of the card to its rear surface.
Preferably, the card module further comprises a first heat transfer pad made of thermally conductive material that is sandwiched between the circuit card and the frame. The pad is designed for enhancing the thermal contact between the frame and the electronic components. Therefore, the kind of material of which its pad is made and its thickness are to be chosen so as to ensure the provision of a thermal contact between the pad and the electronic components having various heights. Thus, it is preferable that the pad material is a soft viscoelastic material and it may even be in the form of a gel.
The card module may further comprise at least one mezzanine card as the circuit card. The mezzanine card is attached to said frame so that the frame is sandwiched between the main card and the mezzanine card, the latter being electrically connected to said main card via at least one connector arranged in said frame. The frame is thus adapted to be in thermal contact with electronic components of the mezzanine card to withdraw therefrom heat generated by these components. Preferably, the module further includes a second pad made of thermally conductive elastic material, to be sandwiched between the mezzanine circuit and the frame.
Preferably, the frame has a base surface adapted to be in thermal contact with said electronic components on the front surface of the circuit card and at least two peripheral side walls adapted to be in thermal contact with the edge areas of the front surface of the circuit card. Preferably, the frame has side walls all along the circumference of the base surface so that, if the main card does not have electronic components on its rear surface, its sealing may be achieved by simple attaching said card to the frame. When the rear surface of the circuit card also bears heat generating electronic components, a rear cover should be attached to the frame. A front cover should be used when the mezzanine card has such components on its rear surface. When the rear surfaces of the main and mezzanine cards bear heat generating electronic components, the front and rear covers may serve to transfer heat generated thereby to said frame.
For sealing the main card and, optionally, the mezzanine card in the module, the latter should comprise both rear and front covers attached to said frame, with appropriate gasket sandwiched therebetween. When the module is hermetically sealed, it is protected from humidity and it may be used when there are severe requirements for protection from any harsh environment.
Preferably, both the main card and the mezzanine card of the module meet requirements of a specific standard, and said thermally conductive frame meets corresponding requirements of mechanical specifications of said standard.
In accordance with another aspect of the present invention, there is provided a method of utilizing a convection cooled circuit card for producing a conduction cooled electronic card module.
In accordance with a still further aspect of the present invention, there is provided a kit comprising a convection cooled circuit card and parts to be assembled therewith for producing a conduction cooled card module according to the present invention and a convection cooled card module, both adapted for insertion into a corresponding chassis of an electronic device.
The present invention provides for a conduction cooled card module, which is based on a convection cooled card and is, therefore, much simpler in production and cheaper than the conduction cooled card modules. The significance of the present invention goes beyond the preparation of highly reliable, stable, and cost-effective conduction cooled card modules meeting standard requirements. Since the card modules may be sealed, the modules retain superior performance in harsh environments. The products are better suited for applications needed for ruggedization (for example, the ability to withstand shock and vibration). Additionally, the modules are better suited in systems needed for extended temperature operation and in life-critical and quality-sensitive applications.